In my British Pat. No. 1,475,822 published June 10th 1977, there is proposed an articulated road vehicle having an engine mounted on a tractor unit of the vehicle at a position to the rear of the axis of a fifth wheel coupling between the tractor unit and a semi-trailer unit. I included in the aforesaid specification a diagrammatic representation of a tractor unit having a chassis, a driven rear axle and a further rear axle to the rear of the driven axle. I further represented diagrammatically an engine disposed partly between wheels of the non-driven rear axle and connected by a shaft with a differential housing of the driven axle.
In known tractor units for articulated vehicles of the general kind disclosed in the aforesaid specification, a unit comprising the engine and a gearbox is mounted by means of resilient mountings on a chassis of the tractor unit, is spaced significantly along the tractor unit from the driven axle and is connected with a differential of the driven axle by a shaft incorporating universal joints. While this arrangement is suggested by the diagrammatic representations in the aforesaid specification, I have found that the suggested arrangement can be improved by supporting the engine and gearbox unit on the rear axles, rather than supporting the engine and gearbox unit entirely on the chassis of the tractor unit.
Supporting of a vehicle engine and gearbox on an axle of the vehicle has been proposed in the prior art. British Pat. No. 291,251 Budge discloses a passenger car having a front axle connected by leaf springs with a chassis of the vehicle. A unit comprising an engine and a gearbox is supported at one end of the unit on the front axle and at the other end of the unit on the chassis by means of a ball and socket joint. This joint permits the engine and gearbox unit to tilt laterally with the front axle relative to the chassis.
In U.S. Pat. No. 3,115,206 of Renner and in German Pat. No. 1,917,563 of Rosenkrands, there is proposed an arrangement similar to that of Budge for the rear of a passenger car. These patents disclose an engine and gearbox unit which is rigidly connected with an axle and is connected with a chassis by a linkage which permits lateral tilting of the engine with the axle relative to the chassis. In each vehicle proposed in these patents, the engine projects rearwardly from the rearmost axle of the vehicle. It has been found that this arrangement impairs stability of the vehicle, particularly in unusual circumstances, for example when the vehicle skids laterally.
U.S. Pat. No. 1,975,366 of Linderman discloses a four-wheeled motor vehicle having a chassis and further having a sub-frame which carries the vehicle engine. The sub-frame is connected at its front end with the vehicle chassis by leaf springs and is connected at its rear end with the chassis by means of a further leaf-spring. Accordingly, the engine is free to move on the leaf-springs of the sub-frame relative to the chassis of the vehicle.
The particular arrangement proposed in the aforementioned prior art for passenger cars are clearly not useful in modern road vehicles intended for carrying large amounts of freight and do not enable the weight distribution proposed in my aforesaid British patent to be achieved in an articulated, freight carrying road vehicle.
In U.S. Pat. No. 2,013,599 of Butler, there is discloased a motor vehicle having a chassis and a driven axle which is connected with the chassis by means of a flexible sub-frame. A rigid unit comprising the engine and gearbox is connected at one of its ends directly with the differential housing of the driven axle and is connected at its opposite end with the flexible subframe. Accordingly, both the driven axle and the engine participate in movement of the sub-frame relative to the chassis and movement of the engine relative to the driven axle is avoided.
A tractor unit of an articulated motor vehicle is disclosed in U.S. Pat. No. Re. 28675 of Hobbensiefken. This tractor unit has a single rear axle and the patent emphasizes that the provision of a third axle is avoided. A sub-frame on which are mounted an engine, a gearbox and the driven rear axle is connected with a chassis of the vehicle by a hitch. The engine and gearbox form a unit which is disposed forwardly of the driven axle and is connected therewith by a shaft incorporating universal joints. The Hobbensiefken patent teaches that central mounting of the engine and related components substantially increases pay load capacity by improving weight distribution.